1. Field of the Invention
This invention relates to magnetostrictive wires having uniaxial magnetic anisotropy and to methods of manufacture thereof.
2. Description of the Prior Art
U.S. Pat. No. 3,820,090 of Wiegand describes a bistable ferromagnetic wire of generally uniform composition having a central magnetically soft core and a magnetically hard outer shell portion of substantially the same chemical composition. The wire is made by starting with 48:52 Fe:Ni alloy wire, stretching 21/2% and then circumferentially straining the wire as by twisting the wire back and forth with or without retaining a permanent twist.
U.S. Pat. No. 3,217,301 of Shook describes a process of stretching a segment of a wire along its length by suspending a heavy weight from it while electroplating the wire with a ferromagnetic nickel coating with negative magnetostriction (i.e., which is increased by compression following plating upon release of the weight causing the stretching). The substrate is composed of a conductive metal such as an alloy of Cu, Al, brass, or bronze. Sonic pulses are generated by a read coil on the unstressed end of the wire, because of its sensitive magnetostrictive properties, for propagating a sonic stress wave through the memory element. Sections of the stressed magnetostrictive coating are used to store bianary data, and helical "sense coils" along the element sense nondestructively the data in response to such an acoustic wave. Domains are written by means of helical "write coils."
U.S. Pat. Nos. 3,129,412 of Lovell and 3,145,372 of Suits et al teach provision of a rectangular thin film delay line structure with a thin NiFe (85:15 or 75:25) magnetostrictive film having a transverse magnetic anisotropy (easy axis). Acoustic waves are generated at one end of the substrate and data is introduced at one end of the strip. The magnetostrictive effects caused by the acoustic wave acting on the thin film generates a phased delay along the delay line. No suggestion of prestressing of the substrate is involved, nor is any spiral or twisting involved.
U.S. Pat. No. 3,492,667 of Gratian describes a magnetic memory element with a hollow tube of magnetostrictive material such as 60:40-NiFe which transmits acoustic waves for reading or writing data.
U.S. Pat. No. 3,534,340 of Murray et al shows in FIG. 10 a magnetostrictive rod 100, having a traveling domain wall, juxtaposed axially with a sheet of magnetic storage medium 104 magnetized transversely. However, there is no prestressing of the rod 100, nor is a large pulse provided by the rod.
U.S. Pat. No. 3,548,390 of Furuoya for a semi-permanent memory device describes a wire having a core of a soft film coated by a hard film. It was intended to replace a twistor wire, with circumferential magnetization, plus another NiFe soft films.
U.S. Pat. No. 3,370,979 of Schmeckenbecher teaches provision of a structure with a cylindrical Permalloy storage layer 11 of Ni-Fe-P on a glass substrate 17, coated with an outer biasing layer 13 of Ni-Co-Fe-P.
Bartkus et al U.S. Pat. No. 3,134,096 in FIG. 5 shows a hollow cylinder with an inner core 10 of 6.0 CrO, 54.0 MnO, 40.0 Fe.sub.2 O.sub.3 and 0.9 Br/Bs as described in U.S. Pat. No. 2,950,252, with an outer layer 34 of high coercivity material.
Matsushita U.S. Pat. No. 3,451,793teaches an inner cylindrical conductive core, coated with a layer of NiFe (50:50) covered by a layer of NiFe (79:21).
None of the above prior art suggests providing a diagonal angle of magnetic anisotropy relative to the axis of a cylindrical or flat substrate where plating is involved. This is a crowded art and the teaching of Wiegand U.S. Pat. No. 3,820,090 leads away from this disclosure because it teaches stretching and repeated twisting back and forth of a material, thereby yielding work hardening and magnetic hardening, but requires that there be only one material included. It also requires that the core be of the same magnetic material as the outer shell of the wire. With this invention, devices can be made without any mechanical stress being employed to impart a helical anisotropy to a magnetostrictive element.